Flicker detection device, flicker elimination device, image pickup device, and flicker detection method

ABSTRACT

A flicker detection device includes an accumulation section that divides a screen into a plurality of areas to perform accumulation of pixel levels, writing and reading of the accumulation result to and from a memory area allocated to every area, thereby accumulating the pixel levels in the area for every area, an accumulation result memory that stores the accumulation results of the accumulation section, an area discrimination section that discriminates whether or not every area is a still image area using the accumulation result obtained by the accumulation section and the accumulation result stored in the accumulation result memory, and a flicker level calculation section that averages the accumulation results of the areas discriminated as the still image area by the area discrimination section, and performs an operation using the averaged accumulation result and the accumulation result obtained by the accumulation section, thereby calculating a flicker level.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2005-250313 filed in the Japan Patent Office on Aug. 30,2005, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a flicker detection device, a flickerelimination device, an image pickup device, and a flicker detectionmethod. In detail, a screen is divided into a plurality of areas,addition of pixel levels and writing and reading of the result of theaddition to a memory area allocated to each area are performed, thepixel levels in the area are accumulated for every area, and whether ornot the area is a still image area is discriminated for every area usingthe result of the accumulation and an accumulation result of the samearea which has already been stored in an accumulation result memory.Further, the accumulation results of the areas discriminated as stillimage areas are averaged, and a flicker level is calculated for everyscreen based on the averaged accumulation result and the accumulationresults obtained by accumulating the pixel level in each of the areasfor every area, thereby removing flickers.

2. Related Art

In the case in which image pickup is performed under a light sourceperiodically turning on and off such as a fluorescent light, there arecaused periodical bright and dark fringes on the pickup image orperiodical differences in brightness of whole image between the frames.These are called flickers, and considered to be an inevitable problemunder the blinking light source for image pickup devices equipped withimage sensors accumulating charges to generate video signals.

In an image sensor, there can be different charge accumulation timingsfor every plane or for every line, and a method of synchronizing thecharge accumulation timings for every plane is called a global shuttermethod while a method of synchronizing the charge accumulation timingsfor every line is called a rolling shutter method.

In the global shutter method, if the image pickup rate is higher thanthe blinking frequency of the light source, the amount of chargeaccumulated in a frame period varies between the frames, which may causea flicker.

FIG. 7 is a diagram for explaining the charge accumulation amount in theimage sensor adopting the global shutter method. In the case in whichthe illumination intensity IL periodically varies as shown in FIG. 7 inaccordance with the frequency of the commercial power supply voltage,the difference in phase between the periodical illumination intensityand the exposure period causes the area difference between the hatchedareas with a constant exposure period TC. The area of the hatched areacorresponds to the charge accumulation amount, and accordingly, thedifference in the areas, namely the difference in the chargeaccumulation amount, causes the difference in brightness between theframes. Therefore, as shown in FIG. 8, the frames with different phasesfrom the illumination intensity IL form a video image with a brightnessdifference between the frames, and periodical differences in brightnessof whole image between the frames appear. It should be noted that inFIG. 8 shows the case in which three frame periods correspond to onecycle of the illumination intensity variation.

A flicker component included in the video image shot under theperiodically blinking light source can be approximated by a sine wave,and a method of removing the flicker utilizing the characteristics ofthe sine wave to form a correction image is adopted. Further, a methodof detecting the flicker component from the input image and controllingthe gain based on the detected flicker component in order for correctingthe flicker has been proposed (see, for example, JP-A-2004-222228).

SUMMARY

Incidentally, the phase and the amplitude of a face flicker can beobtained by performing brightness integration of the whole screen foreach of the screens and then comparing the results of the integrationwith each other using a plurality of screens corresponding to the periodof the screens having the same phase relations to the illuminationintensity variation, namely using the screens with different phases withrespect to the periodic variation of the illumination intensity.

For example, if the period of the illumination variation, namely theflicker period corresponds to three frame periods, the brightnessintegration of the whole screen is performed on the three frames ofscreens with different phase relations to the illumination variationfrom each other. It is assumed here that the result of the brightnessaccumulation of the first frame is “YI=100,” the result of thebrightness accumulation of the second frame is “YI=80,” and the resultof the brightness accumulation of the third frame is “YI=90,” as shownin FIG. 9. In this case, since the average of three frames is “90,” theflicker component of the first frame becomes “FL=10,” the flickercomponent of the second frame becomes “FL=−10,” and the flickercomponent of the third frame becomes “FL=0”.

However, if a moving object is included in the screen of the pickupimage, the result of the brightness accumulation is varied, andaccordingly, the accumulation result does not correctly represent theflicker component.

It is assumed that, for example as shown in FIG. 10, the moving objectOB is included in the pickup image shown in FIG. 9, the accumulationresult of the first frame is “YI=100” with the brightness of the movingobject equal to the brightness of the screen, the accumulation result ofthe second frame including a half of the moving object OB is “YI=85,”and the accumulation result of the third frame including only a littlepart of the moving object OB is “TI=91”. In this case, since the averageof the three frames is “YIavg=92,” the flicker component of the firstframe becomes “FL=8,” the flicker component of the second frame becomes“FL=−7,” and the flicker component of the third frame becomes “FL=−1,”and accordingly, the flicker components become different from the caseshown in FIG. 9.

Therefore, according to an embodiment of the invention, there areprovided a flicker detection device, a flicker elimination device, animage pickup device, and a flicker detection method capable of easilydetecting the flicker level with a simple configuration and alsoremoving the flicker.

According to a flicker detection device, a flicker elimination device,an image pickup device, and a flicker detection method of an embodimentof the invention, a screen is divided into a plurality of areas,accumulation of pixel levels, writing and reading of the accumulationresult to and from a memory area allocated to every area are performed,thereby accumulating the pixel levels in the area for every area, andthe obtained accumulation result is stored in an accumulation resultmemory. In this case, in accumulating the pixel levels, in each of theareas, the pixel levels are sequentially accumulated in a linedirection, the accumulation result is written in the memory areaallocated to every area in response to termination of the accumulationin the line direction, and in accumulating the pixel levels in the linedirection on the subsequent line, the accumulation result from thememory area is read out and the pixel levels are sequentially added tothe accumulation result thus read out, and the accumulation result iswritten back in the memory area allocated to every area in response totermination of the accumulation in the line direction, thereby obtainingthe accumulation result. Further, discrimination whether or not everyarea is a still image area is performed using the accumulation resultobtained by accumulating the pixel levels in the area for every area andthe stored accumulation result. The accumulation results of the areasdiscriminated as the still image area are averaged. For example, theaccumulation results of the areas discriminated as the still image areain the screens having different phases with respect to the illuminationintensity variation from each other are averaged. By performing anoperation using the averaged accumulation result and the accumulationresult obtained by accumulating the pixel levels in the area for everyarea, the flicker level can be calculated.

According to an embodiment of the invention, the accumulation of thepixel levels and writing and reading of the accumulation result to orform the memory area allocated to every area are performed, an operationis performed using the accumulation result obtained by accumulating thepixel levels in the area for every area and the average value of theaccumulation results of the areas discriminated as the still image area,thereby calculating the flicker level. Therefore, the flicker level caneasily be detected even if a moving object is included. Further, sincethe accumulation result is calculated by repeating the writing andreading of the accumulation result to and from the memory area allocatedto every area in obtaining the accumulation result, the accumulationresult can efficiently obtained without requiring large capacity memory.Therefore, the configuration can be simplified, and accordingly, thecost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings, wherein like numbers refer to like elements.

FIG. 1 is a block diagram showing a configuration of an image pickupdevice.

FIG. 2 is a block diagram showing a configuration of a flicker detectionsection.

FIGS. 3A and 3B are diagrams for explaining discrimination operationsfor every pixel and for every area, respectively.

FIG. 4 is a diagram for explaining the operation of an accumulationsection.

FIGS. 5A through 5D are diagrams for explaining the operation of an areadiscrimination section.

FIG. 6 is a flowchart showing a flicker detection elimination operation.

FIG. 7 is a diagram for explaining the charge accumulation amount in theimage sensor adopting the global shutter method.

FIG. 8 is a diagram for explaining the face flicker.

FIG. 9 is a diagram showing brightness accumulation results and flickerlevels.

FIG. 10 is a diagram showing the case in which a moving object isincluded.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. FIG. 1 shows the configurationof an image pickup device.

An image pickup section 11 of an image pickup device 10 generates videosignal Sv and supplies it to an A/D conversion section 12. The A/Dconversion section 12 converts the video signal Sv supplied from theimage pickup section 11 into a digital video signal Dv, and supplies itto a flicker detection section 20 and a flicker correction section 30.The flicker detection section 20 detects the flicker level, and suppliesa flicker level signal Lf representing the detection result to theflicker correction section 30.

FIG. 2 shows the configuration of the flicker detection section. Anaccumulation section 21 of the flicker detection section 20 divides thescreen into a plurality of areas, and calculates accumulation of thepixel levels for every area, namely the brightness levels of the areas.Further, the accumulation section 21 supplies the accumulation resultmemory 22, an area discrimination section 23, and a flicker levelcalculation section 24 with the accumulation results YM.

The accumulation result memory 22 stores the accumulation results YMsupplied therefrom. Further, the area discrimination section 23 issupplied with an accumulation result YM′ which has already beencalculated using the video signal Dv of the frame having the same phasewith respect to the periodic illumination intensity variation as that ofthe frame, from which the accumulation results YM supplied from theaccumulation section 21 to the area discrimination section 23 areobtained.

It should be noted here that, assuming the ratio of the frequency of theillumination intensity variation to the frame frequency is “Ka:Kb,” andthe least common multiple of “Ka” and “Kb” is “Klcm,” the period of theframe images having the same phases with respect to the illuminationintensity variation can be obtained as a period corresponding to “Klcm”frames. Therefore, if the frame frequency is higher than the frequencyof the illumination intensity variation, namely the flicker frequency,the accumulation result YM′ corresponding to the accumulation results YMcan be supplied to the area discrimination section 23 by memorizing theaccumulation results of “Klcm” frames. It should be noted that the framefrequency is obvious from the operation of the image pickup section 11,and the flicker frequency is assumed to be set with a user interface(not shown) provided to the image pickup device 10. Further, it is alsopossible to detect periodicity of the brightness variation in the frameimage to calculate the flicker frequency.

The area discrimination section 23 calculates the difference between theaccumulation result YM supplied from the accumulation section 21 and theaccumulation result YM′ supplied from the accumulation result memory 22for every area in the same position, and discriminates that the area isa moving image area if the difference value exceeds a threshold value,or a still image area if it does not exceed the threshold value.Further, it supplies a flicker level calculation section 24 with adiscrimination signal RD representing the discrimination result.

The flicker level calculation section 24 then generates a flicker levelsignal Lf representing the flicker level of every flame using thediscrimination signal RD and the accumulation result YM, and suppliesthem to the flicker correction section 30. In generating the flickerlevel signal Lf, the accumulation results of the areas denoted as thestill image areas with the discrimination signal RD are averaged. In theaveraging process, the average value of the accumulation results of theframe images having different phases with respect to the periodicalillumination intensity variation from each other. Further, the flickerlevel signal Lf is generated based on the difference between the averagevalue thus calculated and the accumulation result of each frame.

The flicker correction section 30 performs correction of the videosignal Dv in accordance with the flicker signal Lf so as to eliminatethe flicker component, and supplies a camera signal processing section40 with the video signal Dvc processed with the flicker correction.

The camera signal processing section 40 performs various signalprocessing such as a gamma correction or a knee correction on the videosignal Dvc processed with the flicker correction to generate videooutput signal Vout.

The flicker detection elimination operation will now be explained. Asdescribed above, the accumulation section 21 divides the screen into aplurality of areas to obtain the brightness accumulation result forevery area. Hereinafter, for the sake of simplicity of explanation, itis assumed that the size of the screen is 100 pixels in the verticaldirection and 100 pixels in the horizontal direction, the pixel of thevideo signal Dv is composed of 10 bits, and the screen is dividedequally into five blocks in each of vertical and horizontal directions.

If the screen is divided into a plurality of areas to performdiscrimination of whether or not each of the areas is a still imagearea, the capacity of the memory used therefor can be reduced comparedto the case of discriminating whether or not each of the pixels is in astill image area.

For example, in the case in which whether or not each of the pixels isin the still image area is discriminated on the frame image includingthe moving object OB, assuming that the previous frame image GFa isstored, the difference in the pixel level between the frame image GFaand the input frame image GFb is detected in every pixel as shown inFIG. 3A. The pixel section ARm (denoted with hatching) in which thedifference in the pixel level exceeds the threshold value isdiscriminated as the moving image area, and the other pixel section ARsin which it does not exceed the threshold is discriminated as the stillimage area. As described above, in the case of discriminating whether ornot each of the pixel is in the still image area, the memory capacity of“100 pixel×100 pixel×10 bits 100,000 bits” is necessary for storing theframe image GFa.

Further, in the case of discriminating whether or not each areaincluding a plurality of pixels is the still image area on the frameimage including the moving object OB, as shown in FIG. 3B, in storingthe previous frame image GFa, the frame image GFa is divided equallyinto five blocks in each of vertical and horizontal directions to storein the memory the accumulation result of every area. Further, thedifference between the accumulation result stored for every area and theaccumulation result of the area in the corresponding position in theinput frame image GFb is detected. The area section BRm (denoted withhatching) in which the difference in the accumulation results exceedsthe threshold value is discriminated as the moving image area, and theother area section BRs in which it does not exceed the threshold isdiscriminated as the still image area. In this case, since each of theareas can be described with “10 bits×400 pixels=21 bits,” the memorycapacity of “5 blocks×5 blocks×21 bits=525” becomes necessary in totalfor storing the accumulation results of the whole areas of the frameimage GFa.

Therefore, by performing the discrimination of whether or not every areais the still image area, the memory capacity necessary therefor cansubstantially be reduced compared to the case of discriminating whetheror not every pixel is in the still image area.

It should be noted here that in the case of discriminating whether ornot every area is the still image area, the area section BRsdiscriminated as the still image area does not include the image of themoving object OB, and the area section BRm discriminated as the movingimage area includes both the moving object OB and a still image.

Further, since the face flicker is caused by the difference between thecharge accumulation period (exposure period) for one frame and theblinking period of the light source, the variation of pixel level iscaused by the flicker in a constant ratio throughout the pixels in thesame frame. Accordingly, if the level variation caused by other factorsthan the flicker, the flicker level can be detected from only a partialsample in a frame.

Therefore, since it can be said that the still image area, which doesnot include the image of the moving object, is in the condition in whichno other level variation than the flicker is included, the flicker levelcan be detected in the case of discriminating whether or not every areais the still image area with substantially the same accuracy as in thecase of discriminating whether or not each pixel is in the still imagearea.

The operation of the accumulation section 21 will now be explained. Inthe case in which the screen is divided into a plurality of areas tocalculate the accumulation result for every area, the accumulationsection 21 efficiently calculates the accumulation results with a fewmemory capacity by repeatedly using the memory area as described below.

Since the horizontal size of one area is, for example, 20 pixels, asshown in FIG. 4, the accumulation result obtained by accumulating thepixel levels of the first 20 pixels, namely the first through 20thpixels in the first line is written in the memory address 1 of thememory MR. The accumulation result obtained by accumulating the pixellevels of subsequent 20 pixels, namely 21st through 40th pixels in thefirst line is stored in the memory address 2. Similarly as above, theaccumulation result of the 20 pixels to the last of the first line,namely the accumulation result obtained by accumulating 81st through100th pixels in the first line is stored in the memory address 5.

In the second line, the accumulation result stored in the memory address1 is read out, the pixel levels of the first through 20th pixels areadded to the accumulation result thus read out, and the accumulationresult thus obtained is written back in the memory address 1.Subsequently, the accumulation result stored in the memory address 2 isread out, the pixel levels of the 21st through 40th pixels are added tothe accumulation result thus read out, and the accumulation result thusobtained is written back in the memory address 2. Similarly as above,the process of reading out the stored accumulation result from thememory, and writing it back in the memory after adding the pixel levelsin the second line to the accumulation result thus read out isperformed.

Since the vertical size of one area is, for example, 20 lines, byrepeating the similar process to the process of the second line up tothe 20th line, the accumulation results in the areas of the first columncan be stored in the memory address 1 through the memory address 5.

Similarly, regarding the areas in the second column, the accumulationresults in the areas in the second column can be stored in the memoryaddress 6 through the memory address 10 by similarly processing to theareas in the first column using the memory address 6 through the memoryaddress 10.

Regarding the third through fifth columns, the accumulation results inthe areas in the third through fifth columns can be stored in the memoryaddress 11 through the memory address 25 by repeating the similarprocess using the memory address 11 through the memory address 25.

As described above, by assigning one memory address to each of the areasobtained by dividing the screen and storing the accumulation result inthe memory address, the required memory capacity can be reduced comparedto the case of storing the pixel level of each of the pixels is storedin the memory. Further, since the reading and writing processes areperformed once for 20 pixels, there is no need for using high frequency.

The accumulation results YM thus generated are supplied to theaccumulation result memory 22, an area discrimination section 23, and aflicker level calculation section 24. It should be noted that theaccumulation section 21 can be arranged to calculate the accumulationresults using the accumulation result memory 22. In this case, thecondition in which the accumulation results YM are stored in theaccumulation result memory 22 is realized at the time point when thecalculation of the accumulation results is completed.

The discrimination operation of the area discrimination section will nowbe explained with reference to FIGS. 5A to 5D. In the discriminationoperation of whether or not it is the still image area, two frame imageshaving the same phases shown in FIG. 5B with respect to the variation ofthe illumination intensity IL shown in FIG. 5A are used. For example,the accumulation result YM′ of the frame image GF1 of the first framestored in the accumulation result memory 22 and the accumulation resultYM of the frame image GF4 of the fourth frame calculated by theaccumulation section 21 are used.

As described above, in the two frame images having the same phase withrespect to the illumination intensity variation, the flicker componentsbecome the same if there is no level variation caused by other factorsthan the flicker. Therefore, if the accumulation results of the twoframes are compared to each other in the areas in the same positions,the difference therebetween becomes small with no level variation causedby other factors than the flicker, and the difference therebetweenbecomes large with level variation caused by other factors than theflicker.

Therefore, as shown in FIG. 5C, the difference DE (0,0) through DE (4,4)of the accumulation results is obtained for every area in thecorresponding positions of the two frame images GF1 and GF4 having thesame phases with respect to the variation in the illumination intensity,and each of the differences DE (0,0) through DE (4,4) is compared withthe threshold value. It should be noted here that the difference in thearea not including the moving object OB becomes small while thedifference in the area including the moving object OB becomes large.Therefore, as shown in FIG. 5D, the area with the difference exceedingthe threshold value, namely the area including the moving object OB, isdiscriminated as the moving image area (denoted with hatching) BRm.Further, the area with the difference not exceeding the threshold value,namely the area not including the moving object OB is discriminated asthe still image area (area without hatching) BRs. The discriminationoperation of whether or not it is the still image area is thusperformed, the discrimination signal RD representing the discriminationresult is generated and then supplied to the flicker level calculationsection 24.

Further, in FIGS. 5A through 5D, if the moving object is small, in thediscrimination by obtaining the difference in the accumulation resultbetween the two frame images GF1 and GF4, the area through which themoving object has passed is discriminated as the still image area.However, this area is the moving image area including the moving objectin the frame image GF2 or the frame image GF3. Therefore, thediscrimination of whether or not it is the still image area is performedfor every frame image having a different phase with respect to theillumination intensity variation. For example, by performing thediscrimination using the frame images GF2 and GF5 (not shown), or thediscrimination using the frame images GF3 and GF6 (not shown), the stillimage area can correctly be discriminated. Alternatively, it is possiblethat the motion vector of the object is obtained using the frame imagesGF1 and GF4, and the area through which the object has passed betweenthe frame images GF1 and GF4 from the motion vector, thereby judging thearea as the motion area. Further, assuming that the area discriminatedas the moving image area in the frame image GF1 moves to the areadiscriminated as the moving image area in the frame image GF4, if thearea positioned between the area discriminated as the moving image areain the frame image GF1 and the area discriminated as the moving imagearea in the frame image GF4 is processed as the moving image area, thediscrimination can easily be performed.

The flicker level calculation section 24 then generates a flicker levelsignal Lf representing the flicker level of every flame using thediscrimination signal RD and the accumulation result YM. The flickerlevel calculation section 24 calculates the average value averaging thebrightness variation between the frames.

In the calculation of the average value, the frame images havingdifferent phases with respect to the periodical illumination intensityvariation from each other so as to accurately calculate the averagevalue. For example, the frame images GF2 through GF4 are used. Asdescribed above, by using the same numbers of frame images withdifferent phases with respect to the periodical illumination intensityvariation from each other, it can be prevented that the average value iscalculated using only bright frame images or the average value iscalculated using only dark frame images.

Further, in each of the frame images, the accumulation results of theareas discriminated as the area without the level variation caused byother factors than the flicker, namely the still image area isaccumulated to calculate the average value. It should be noted here thatan equal number of accumulation results are used in each of the frameimages so that the average value can easily be calculated. Further, byusing the accumulation results of the areas in the positionsdiscriminated as the still image area in every frame image, it isguaranteed that an equal number of accumulation results are used fromevery frame image.

As described above, by performing accumulation using an equal number ofaccumulation results from every frame images, and dividing by the numberof frames, the average value averaging the brightness variation betweenthe frames caused by the flicker can easily be calculated.

Subsequently, the flicker level of every frame image is calculated usingthe average value thus calculated and the accumulation result of everyframe image. In this case, while calculating the average value using anequal number of accumulation results from every frame image, theaccumulation results used for calculating the average value areaccumulated for every frame, and the difference between thisaccumulation value and the calculated average value is calculated forevery frame. This difference corresponds to an accumulation result ofthe flicker levels of the pixels in the areas from which theaccumulation results used for calculating the average value areobtained. Therefore, by dividing the difference by the number of thepixels in the areas from which the accumulation results used forcalculating the average value are obtained.

Further, since the pixel level variation is caused by the flicker in theconstant rate through out the frame image, it is possible that the frameimages having the different phases with respect to the illuminationintensity variation from each other are used, one of the areasdiscriminated as the still image area is selected from every frameimage, and the average value is calculated using the accumulationresults of the selected areas. In this case, by calculating thedifference between the calculated average value and the accumulationresult used for calculating the average value for every frame, anddividing the difference by the number of the pixels in an area, theflicker level for one pixel can easily be calculated.

As described above, the flicker level for one pixel is calculated forevery frame image, the flicker level signal Lf represents the flickerlevel for every pixel is generated and then supplied to the flickercorrection section 30.

Based on the flicker level signal Lf detected by the flicker detectionsection 20, the flicker correction section 30 corrects the signal levelof the video signal Dv for every pixel so as to eliminate the flicker togenerate the video signal Dvc. It should be noted here that the flickerlevel represents the changed portion of the brightness with respect tothe average value. Therefore, the signal level of the video signal Dv iscorrected to be decreased for the flicker level if the brightness ishigher than the average value, while the signal level of the videosignal Dv is corrected to be increased for the flicker level if thebrightness is lower than the average value, thus the video signal Dvcfrom which the flicker is eliminated can be generated.

As described above, by performing various processes by the camera signalprocessing section 40 on the video signal Dvc from which the flicker iseliminated, the video output signal Vout without the flicker can beobtained even in the case in which the light source causes blinking in apredetermined period.

Incidentally, the flicker level detection process and the flickerelimination process can also be performed by software. In this case, itis assumed that the program is previously stored in the memory,previously recorded in the recording medium and retrieved therefrom tothe memory, or delivered through the network and then stored in thememory, and the central processing unit (CPU) reads the program storedin the memory to execute it.

FIG. 6 is a flowchart showing the flicker detection and eliminationprocess. In the step ST1, the CPU performs an area segmentation processto divide each of the frame images into a plurality of areas.

In the step ST2, the CPU performs an accumulation process to accumulatethe pixel levels in the area to obtain the accumulation result for everyarea.

In the step ST3, the CPU performs an accumulation result storing processto store the accumulation results obtained in the step ST2 in thememory.

In the step ST4, the CPU performs an area discrimination process. In thearea discrimination process, the CPU calculates the difference of theaccumulation result for every area using the accumulation results of thetwo frame images having the same phases with respect to the illuminationintensity variation, namely the accumulation result obtained in the stepST2 and the accumulation result stored in the memory. If the differencedoes not exceeds a threshold value, the area is discriminated as thestill image area, and if the difference exceeds the threshold value, thearea is discriminated as the moving image area.

In the step ST5, the CPU performs an average value calculation process.In the calculation of the average value, the accumulation results of theareas discriminated as the still image area in the area discriminationprocess in the step ST3 are averaged to calculate the average value.

In the step ST6, the CPU performs level calculation process. In thelevel calculation process, the CPU performs an operation using theaverage value calculated in the step ST4 and the accumulation results ofthe areas discriminated as the still image area in the areadiscrimination process in the step ST3 to calculate flicker level for,for example, every pixel for every frame.

In the step ST7, the CPU performs a flicker correction process. In theflicker correction process, based on the flicker level calculated in thestep ST5, the CPU corrects the signal level of the video signal so as tocancel the flicker level.

It should be noted that although in the above embodiment, the case inwhich the flicker is detected and then eliminated after the image ofevery frame is divided into a plurality of areas is explained, the faceflicker caused in the image for every field can also be eliminated byperforming the similar process to the above.

As described above, since one screen is divided into a plurality ofareas, the pixel levels in the area is accumulated for every area,whether or not the area is the still image area is discriminated usingthe obtained accumulation result, and the flicker level is calculatedusing the accumulation results in the area discriminated as the stillimage area, the flicker level can correctly be detected even if themoving object is included in the screen. Further, since the signal levelis corrected in accordance with the detected flicker level, the flickercan accurately be eliminated.

Further, since accumulation results can efficiently be obtained withoutusing a large capacity memory by assigning one memory address to onearea and repeating writing and reading of the accumulation value inperforming accumulation of the pixel levels, the configuration can besimplified, thus reducing the cost.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A flicker detection device comprising: anaccumulation section that divides each image frame of successive imageframes, captured via global shuttering, into a plurality of image areasto perform accumulation of pixel levels, respective pairs ofnon-successive image frames being captured in phase with respect to afrequency cycle of a periodic illumination causing flicker, theaccumulation section writing and reading accumulation data to and from amemory area allocated to the plurality of image areas to accumulatepixel levels in the memory area as accumulation results; an accumulationresult memory that stores the accumulation results of the accumulationsection; an area discrimination section that discriminates whether ornot each of the plurality of image areas is a still image area using anaccumulation result obtained by the accumulation section associated witha first image frame of one of the pairs of non-successive image framesand a previous accumulation result stored in the accumulation resultmemory associated with a second image frame of said one of the pairs ofnon-successive image frames; and a flicker level calculation sectionthat calculates a flicker level by averaging accumulation resultsassociated with image areas discriminated as still image areas by thearea discrimination section to obtain an averaged accumulation result,and by performing an operation using the averaged accumulation resultand the accumulation result obtained by the accumulation sectionassociated with the first image frame of said one of the pairs ofnon-successive image frames.
 2. The flicker detection device accordingto claim 1, wherein the accumulation section performs accumulation ofpixel levels by sequentially accumulating pixel levels in a linedirection, writing accumulation data in the memory area allocated to theplurality of image areas in response to termination of pixelaccumulation in the line direction, reading accumulation data from thememory area and sequentially adding pixel levels of a subsequent line tothe read accumulation data to accumulate pixel levels in the linedirection of the subsequent line, and writing the accumulation data inthe memory area in response to termination of the accumulation in theline direction regarding the subsequent line.
 3. The flicker detectiondevice according to claim 1, wherein the flicker level calculationsection performs the averaging using accumulation results of imageframes with different phases with respect to illumination intensityvariation from each other.
 4. The flicker detection device according toclaim 1, wherein the plurality of image areas form a plurality ofrectangular blocks of pixels that are arranged horizontally andvertically in the image frame.
 5. The flicker detection device accordingto claim 1, wherein plural image frames are between each of said pairsof non-successive image frames.
 6. The flicker detection deviceaccording to claim 1, wherein said flicker level calculation sectioncalculates the flicker level based on a set of the successive imageframes, the set of successive image frames excluding the second imageframe of said pair of non-successive image frames and including thefirst image frame of said pair of non-successive image frames and allimage frames between said first and second image frames.
 7. The flickerdetection device according to claim 1, wherein the accumulation resultmemory includes the memory area allocated to the plurality of imageareas for accumulating the pixel levels as accumulation results.
 8. Theflicker detection device according to claim 1, wherein discriminationregarding whether or not each of the plurality of image areas is a stillimage area is based on a motion vector associated with the first andsecond image frames of said pair of non-successive image frames.
 9. Aflicker elimination device comprising: a setting section that sets afrequency of a periodic illumination causing flicker; an accumulationsection that divides each image frame of successive images frames,captured via global shuttering, into a plurality of image areas toperform accumulation of pixel levels, respective pairs of non-successiveimage frames being captured in phase with respect to the frequency ofthe periodic illumination causing the flicker, the accumulation sectionwriting and reading accumulation data to and from a memory areaallocated to the plurality of image areas to accumulate pixel levels inthe memory area as accumulation results; an accumulation result memorythat stores the accumulation results of the accumulation section; anarea discrimination section that discriminates whether or not each ofthe plurality of image areas is a still image area using an accumulationresult obtained by the accumulation section associated with a firstimage frame of one of the pairs of non-successive image frames and aprevious accumulation result stored in the accumulation result memoryassociated with a second image frame of said one of the pairs ofnon-successive image frames; a flicker level calculation section thatcalculates a flicker level by averaging accumulation results of imageareas discriminated as still image areas by the area discriminationsection to obtain an averaged accumulation result, and by performing anoperation using the averaged accumulation result and the accumulationresult obtained by the accumulation section associated with the firstimage frame of said one of the pairs of non-successive image frames; anda flicker correction section that corrects a pixel level in the firstimage frame of said one of the pairs of non-successive image framesusing the calculated flicker level.
 10. The flicker elimination deviceaccording to claim 9, wherein the plurality of image areas form aplurality of rectangular blocks of pixels that are arranged horizontallyand vertically in the image frame.
 11. The flicker elimination deviceaccording to claim 9, wherein plural image frames are between each ofsaid pairs of non-successive image frames, said flicker levelcalculation section calculates the flicker level based on a set of thesuccessive image frames, the set of successive image frames excludingthe second image frame of said pair of non-successive image frames andincluding the first image frame of said pair of non-successive imageframes and all image frames between said first and second image frames,and the accumulation result memory includes the memory area allocated tothe plurality of image areas for accumulating the pixel levels asaccumulation results.
 12. The flicker elimination device according toclaim 9, wherein discrimination regarding whether or not each of theplurality of image areas is a still image area is based on a motionvector associated with the first and second image frames of said pair ofnon-successive image frames.
 13. An image pickup device comprising: animage pickup section that generates a video signal of a pickup image; asetting section that sets a frequency of a periodic illumination causingflicker on the video signal; an accumulation section that divides eachimage frame of multiple successive image frames of the video signal,captured via global shuttering, into a plurality of image areas toperform accumulation of pixel levels, respective pairs of non-successiveimage frames being captured in phase with respect to the frequency ofthe periodic illumination causing the flicker, the accumulation sectionwriting and reading accumulation data to and from a memory areaallocated to the plurality of image areas to accumulate pixel levels inthe memory area as accumulation results; an accumulation result memorythat stores the accumulation results of the accumulation section; anarea discrimination section that discriminates whether or not each ofthe plurality of image areas is a still image area using an accumulationresult obtained by the accumulation section associated with a firstimage frame of one of the pairs of non-successive image frames and aprevious accumulation result stored in the accumulation result memoryassociated with a second image frame of said one of the pairs ofnon-successive image frames; a flicker level calculation section thatcalculates a flicker level by averaging the accumulation results ofimage areas image areas discriminated as still image areas by the areadiscrimination section to obtain an averaged accumulation result, and byperforming an operation using the averaged accumulation result and theaccumulation result obtained by the accumulation section associated withthe first image frame of said one of the pairs of non-successive imageframes; and a flicker correction section that corrects a pixel level inthe first image frame of said one of the pairs of non-successive imageframes using the calculated flicker level to eliminate a flickercomponent form the video signal generated in the image pickup section.14. The image pickup device according to claim 13, wherein the pluralityof image areas form a plurality of rectangular blocks of pixels that arearranged horizontally and vertically in the image frame.
 15. The imagepickup device according to claim 13, wherein plural image frames arebetween each of said pairs of non-successive image frames, said flickerlevel calculation section calculates the flicker level based on a set ofthe successive image frames, the set of successive image framesexcluding the second image frame of said pair of non-successive imageframes and including the first image frame of said pair ofnon-successive image frames and all image frames between said first andsecond image frames, and the accumulation result memory includes thememory area allocated to the plurality of image areas for accumulatingthe pixel levels as accumulation results.
 16. The image pickup deviceaccording to claim 13, wherein discrimination regarding whether or noteach of the plurality of image areas is a still image area is based on amotion vector associated with the first and second image frames of saidpair of non-successive image frames.
 17. A flicker detection methodcomprising the steps of: dividing each image frame of successivecaptured image frames, captured via global shuttering, into a pluralityof image areas, respective pairs of non-successive image frames being inphase with respect to a frequency cycle of a periodic illuminationcausing flicker; accumulating pixel levels by adding the pixel levelsand writing and reading accumulation data to and from a memory areaallocated to the plurality of image areas to accumulate pixel levels inthe memory area as accumulation results; storing the accumulationresults obtained in the accumulating step; discriminating whether or noteach of the plurality of image areas is a still image area using anaccumulation result obtained in the accumulating step associated with afirst image frame of one of the pairs of non-successive image frames anda previous accumulation result stored in the storing step associatedwith a second image frame of said pair of non-successive image frames;averaging accumulation results of image areas discriminated as stillimage areas in the discriminating step to obtain an averagedaccumulation result; and calculating a flicker level in the first imageframe of said pair of non-successive image frames by performing anoperation using the averaged accumulation result and the accumulationresult obtained in the accumulating step associated with the first imageframe of said pair of non-successive image frames.
 18. The flickerdetection method according to claim 17, wherein the plurality of imageareas form a plurality of rectangular blocks of pixels that are arrangedhorizontally and vertically in the image frame.
 19. The flickerdetection method according to claim 17, wherein plural image frames arebetween each of said pairs of non-successive image frames, thecalculating the flicker level step is based on a set of the successiveimage frames, the set of successive image frames excluding the secondimage frame of said pair of non-successive image frames and includingthe first image frame of said pair of non-successive image frames andall image frames between said first and second image frames, and theaccumulation result memory includes the memory area allocated to theplurality of image areas for accumulating the pixel levels asaccumulation results.
 20. The flicker detection method according toclaim 17, wherein discrimination regarding whether or not each of theplurality of image areas is a still image area is based on a motionvector associated with the first and second image frames of said pair ofnon-successive image frames.